Russia announced Saturday it is expelling 23 British diplomats and threatened further retaliatory measures in a growing diplomatic dispute over a nerve agent attack on a former spy in Britain.

Britain’s government said the move was expected, and that it doesn’t change their conviction that Russia was behind the poisoning of ex-agent Sergei Skripal and his daughter in the English city of Salisbury. Prime Minister Theresa May said Britain will consider further retaliatory steps in the coming days alongside its allies.

The Russian Foreign Ministry ordered the 23 diplomats to leave within a week. It also said it is ordering the closure in Russia of the British Council, a government-backed organization for cultural and scientific cooperation, and is ending an agreement to reopen the British consulate in St. Petersburg.

Video footage posted on social media showed Mr Navalny appearing on Moscow's main thoroughfare, a few hundred metres from the Kremlin, to join several hundred supporters taking part in the nationwide protest, which authorities had said was illegal.

He had only walked a short distance when he was surrounded by helmet-clad police officers.

They wrestled him to the ground on the pavement, and then dragged him feet first into the patrol wagon, the video footage showed.

Mr Navalny's personal Twitter feed carried a post to his followers saying he had been arrested.